The present invention relates generally to the separation of particulates from colloidal suspensions, and more particularly to methods and apparatus for the separation of cellular components from blood to provide blood plasma.
The separation of particulates from colloidal suspensions is usually accomplished by either centrifugation or filtration. While centrifugation is relatively time consuming and requires relatively costly equipment, it is presently the only technology practical for the separation of small sample sizes, typically 5 mL and below. Filtration is substantially faster and more economic, but colloidal particles cause severe fouling and plugging of the filter membrane. Although such plugging can be at least partially overcome by utilizing a continuous shear flow over the membrane or pulsatile flow through the membrane, such approaches are not suitable for the-filtration of small volumes. Thus, it would be desirable to provide improved methods for the filtration of colloidal suspensions. It would be particularly desirable if such methods allowed the filtration of relatively small sample sizes below about 5 mL without plugging.
Most medical diagnostic testing is performed on small samples of blood plasma or serum. As blood is a colloidal suspension of cellular components in plasma, whole blood samples (which are generally on the order of several mL) are presently clotted and centrifuged in order to obtain blood serum prior to testing. Such clotting and centrifugation generally takes about 10 minutes or longer and requires the use of a relatively costly centrifuge. The use of filtration to prepare plasma from such small blood samples would be desirable as it is a more rapid and less costly procedure, generally requiring fewer steps than centrifugal separation of serum. The inability of present filtration technology to adequately separate such small volume colloidal suspensions, however, renders filtration impractical.
For these reasons, it would be desirable to provide improved filtration methods capable of separating particles from colloidal suspensions without suffering from deleterious plugging of the filter membrane. It would be particularly desirable if such methods could handle very small sample volumes, preferably 5 mL and below, and more preferably 100 .mu.L and below. The filtration methods should be rapid and require only relatively inexpensive equipment to be performed. The methods should further be suitable for automated sample handling, requiring a minimum number of manual steps. In the case of plasma preparation from whole blood, it would be desirable if user exposure to the blood could be limited or avoided entirely, and that the plasma obtained be free from hemolysis and other degradation.